The invention concerns a pipe switch for two-cylinder thick material pumps with a pivot pipe pivotable in front of a two-opening wear plate on the cylinder side, with a wear ring which can be pressed against the wear plate in the rim area of the opening by the hydrostatic pressure present inside the pivot pipe, the wear ring capable of limited axial displacement at the end of the pivot pipe on the cylinder side, the wear ring having a centering portion guided on an axis-parallel centering surface of the pivot pipe as well as a sealing part resting against the wear plate via an abutment surface on the cylinder side, wherein the pivot pipe and the sealing part of the wear ring have opposing annular surfaces which are axially spaced from one another thereby forming an annular gap open towards the inside of the pipe, and with a ring arrangement comprised at least in part of a rubbery elastic material axially spanning the annular gap, the ring arrangement with its respective abutment surfaces lying preferably in a pre-stressed manner against each of the annular surfaces.
Tubular branching systems of this kind, which have an automatically hydrostatic adjusting wear ring, are known (DE-A 26 14 895, EP-B 0 656 995). In the annular space there is a rubber elastic ring, which is provided for sealing the gap formed between the centering part and the centering surface and additionally performs a spring function for pressing the sealing part of the wear ring against the wear plate. In practice it has been found that during operation cement deposits form in the area of the radial plane oriented ring surfaces, which despite a material removal in the area of the sealing part and the wear plate could lead to an uncontrolled narrowing of the annular space and to a wearing out of the rubber elastic ring, with a result, that the rubber elastic ring can be pressed out, towards the inside of the pipe, and can be lost.
Beginning therewith it is the task of the present invention to improve the known pipe switch of the above-described type in such a manner, that the rubber elastic material of the ring arrangement is not subjected to excessive wear.
The inventive solution is based on the concept, that the rubber elastic material is to be protected from the abrasive effect of the cement with suitable means. In order to achieve this, it is proposed in accordance with a first inventive embodiment, that the ring arrangement at least on its surface facing the centering part of the wear ring has an axial ring overlay of a wear retardant material which is stiffer than the rubber elastic material. Preferably the ring overlay is comprised of metal, of a metal or textile fabric, of plastic, or of hard rubber. The ring overlay can be adhered to or vulcanized onto the rubber elastic material.
An alternative or advantageous embodiment of the invention envisions that the ring arrangement includes at least two rings of rubber elastic material separated from each other by a hard intermediate ring. The intermediate ring is preferably formed as a metallic ring disk, which has the same inner and outer diameter as the rubber elastic rings. The intermediate ring can be loosely introduced in the ring space between the rubber elastic rings and be provided with multiple through holes separated from each other in angular separation. Preferably the rubber elastic rings are connected to each other via multiple axially parallel pins arranged in angular separation from each other, which pins extend through the through holes in the intermediate ring.
According to a preferred embodiment of the invention the rubber elastic rings are vulcanized onto the intermediate ring at their respective contacting surfaces.
A further alternative or advantageous embodiment of the invention envisions that the ring arrangement is formed by a rubber elastic ring with a co-axial helical spring vulcanized therein. The helical spring is preferably comprised of spring steel and can be introduced into the rubber elastic ring pretensioned under pressure. In the later case the rubber elastic material is expanded by the helical coil spring in the loose ring arrangement, so that in the assembled condition pretensioned within the annular space a supplemental adjustment means is made available.
According to a further alternative or advantageous embodiment of the invention it is proposed that the ring surface adjacent the centering part in a known manner exhibits an annular step formed by a recess facing in the direction of the centering part, undercut with respect to the inside of the pipe, and that a ring seal of elastomeric material separate from the ring arrangement is seated in the annular step. The ring seal has the task of preventing a passage of material through the centering gap, and thereby to minimize the cement deposit on the ring surface facing the centering gap. The ring seal is preferably over-dimensioned with respect to the annular step, which is so dimensioned, that the ring seal is pressed in the annular step under the pretension of the ring arrangement. The ring seal can thereby either exhibit a quadrilateral, in particular, a square cross-section or a round or oval cross-section. Since the inside of the annular step is completely enclosed, it is possible to use therefore a soft elastic material without stiffening. The ring arrangement could in this case be comprised of a one-piece elastomeric ring with a stiffening insert, for example a metal ring.
For sealing the ring gap in the centering surface, in accordance with an advantageous or alternative design of the invention a ring notch can be provided in the centering surface of the pivot pipe or in the centering part of the wear ring, for receiving a ring seal for bridging the annular gap between the centering surface and the centering part.
In order to guarantee a reliable sealing of the ring space over a long operating time, it is proposed in accordance with a further advantageous or alternative embodiment of the invention to have a tensioning mechanism provided between the pivot pipe and wear ring, with which the pretensioning of the ring arrangement can be adjusted. The tensioning mechanism preferably includes at least two, more preferably three tensioning screws distributed about the circumference of the pivot pipe and displaceable axially parallel with respect to the pivot pipe, each tensioning screw engaging respectively in an axis-parallel oriented thread of the wear ring. The tensioning screws are preferably formed as set screws guided with their shaft respectively in a rim open axial guide of the pivot pipe and their head is supported against a shoulder bordering against the axial guide.